Table saws of various designs include a frame and an upper surface having an opening through which a blade extends. The upper surface supports a material, such as wood, as it is pushed towards the blade for cutting. Table saws have traditionally been stand-alone pieces of equipment that are used in workshops. Because most stand-alone table saws are used in large open spaces, the dimensions of the table saw can be large enough to support materials of various sizes for cutting. Tables that are used in workshops are not readily moved from one location to another. At construction sites, it is useful to have a table saw that can be easily moved from one location to another or between different construction sites. Accordingly, smaller and portable table saws have been designed. These table saws use lighter materials and have reduced the dimensions of the frame and the upper surface to reduce the size and weight of the table saw thereby creating the desired portable table saw. The portable table saws also use a separable folding stand to hold the table saw at the correct height for operation.
An integral part of most table saws is a movable rip fence. The rip fence is positioned perpendicular to the upper cutting surface and is aligned generally parallel to the position of the blade. Most rip fences are designed to span between the front edge and the rear edge of the upper cutting surface. Moreover, the rip fence can be positioned in any position along the upper surface and is secured in such a position by a locking mechanism. The rip fence is usually secured in a position a given distance away from the blade and can be put on either side of the blade. When the rip fence is secured in a position, the wood can be pushed against the side of the rip fence to slide on the upper surface to be cut by the blade. Thus, accurate and straight cuts can be made.
Rip fences of various different designs are readily known in the prior art. In addition, different methods of securing the rip fence at a given location on the upper surface, including the use of a locking mechanism, are known. One of the primary objectives for the rip fence is for it to be generally parallel to the blade so that the most accurate cuts can be made. It is known that an effective way to make the rip fence parallel with the blade is to force it to be perpendicular to the front and rear edge surfaces of the table saw. Thus, many rip fences use a front locking mechanism and a rear locking mechanism. The front locking mechanism presses against the front edge surface and the rear locking mechanism presses against the rear edge surface. In this way, the locking mechanism aligns the rip fence perpendicular to the edge surfaces and parallel to the blade.
It is also helpful to properly align the rip fence if the front and rear locking mechanism move simultaneously. To achieve this, rip fences typically include a handle which is connected to the front locking mechanism and a rod that connects between the handle and the rear locking mechanism. When the handle is in a first and released position, the front locking mechanism is positioned in a released position relative the front edge surface and the rod reduces pressure and allows the rear locking position to move into a released position relative the rear edge surface. When the handle is in a second and locked position, the front locking mechanism is positioned in a locked position along the front edge surface and the rod pushes the rear locking mechanism into the locked position. As the handle moves from the released to the locked position, the front and rear locking mechanism engage with the front and rear edges at the same time.
Different types of front and rear locking mechanisms are known. Some front locking mechanisms include a cam that is connected to a handle such that when the handle is put into the locked position, the cam is pushed against a surface on the front edge of the table saw to secure the rip fence in position. FIGS. 12-14 depict one type of previously known rip fence in a locked position. The rip fence 120 of FIGS. 12-14 includes a front locking mechanism 122 and a rear locking mechanism 124. The front locking mechanism 122 includes a frame 126, a handle 128, a linkage 130, a cam 132, a lever 134, and a spring plate 136. The handle 128 is pivotally connected to the frame 126 at a pivot point 138, the cam 132 is pivotally connected to the frame 126 at pivot point 140, and the lever 134 is pivotally connected to the frame 126 at point 142. The linkage 130 is attached at one end to the handle 128 and at the other end to the cam 132. The rear locking mechanism 124 includes a frame 142 and a clamping lever 144. The rear clamping lever 144 is pivotally connected to the frame 142 at a pivot point 146. The front and rear locking mechanisms 122, 124 are coupled together by a clamping rod 148 that extends between and connects the lever 134 of the front locking mechanism 122 to the lever 144 of the rear locking mechanism 124.
When the handle 128 is pivoted upwardly from the locked position about pivot point 138, the linkage 130 pulls cam 132 causing the cam 132 to pivot about pivot point 140. The cam 130 is positioned to actuate the lever 134 causing the lever to pivot about pivot point 142. The lever 134 does two things. First, it pushes the spring plate 136 against the front rail (not shown) of the table saw creating a spring force which causes the guide block to be pulled against the rail thus aligning the frame (and the overall fence) with the rail (and the blade). Second, it pulls the clamping rod 148. The clamping rod 148 in turn pivots the rear clamping lever 144 about the pivot point 146 into engagement with the rear guide rail of the table saw.
While effective, there is no separation between the alignment force generated by the spring plate 136 and the locking force generated by the rear clamping lever 144 when locking the fence onto the rails. The spring plate 136 and the rear clamping lever 144 are both controlled by the cam 132 and lever 134 action. Therefore, the system must be balanced between alignment force in the spring and clamping force in the rear clamping lever. An increase in clamping force may result in a decrease in alignment force as the rear of the fence may clamp before the spring creates enough force to move/align the rip fence. Conversely, increasing the alignment force may result in the spring touching the front rail when the system is unlocked which can result in damage to the rail as well as unpleasant noises and/or vibrations when the position of the fence is adjusted.